resolution for the sparse reconstruction based SLIMMER 
algorithm while using TDX data stack. 
As multiple scatterers inside one resolution cell most likely 
occur in high rise urban areas, the situation that two scatterers 
inside one resolution cell (one from the building facade and 
another from the ground) is simulated as an another example to 
evaluate the performance of the spectral estimation methods. 
The building is assumed to have an elevation of 80 m where 
ground is at zero elevation. 
Fig.7 shows the estimated elevation values of the two scatterers 
with MAP (left), NLS (middle) and SLIMMER in TSX (upper) 
and TDX (lower) cases. The x-axis refers to the true elevation 
of scatterers on the building facade. The y-axis shows their 
estimated elevations. The ideal image would be two straight 
lines (one horizontal and another one diagonal). The better 
estimation accuracy shown in the lower plots confirms the fact 
that reconstruction accuracy of tomographic SAR inversion can 
be improved significantly by using jointly fused TerraSAR-X 
and TanDEM-X data. 
5. CONCLUSION & OUTLOOK 
This paper presents the first demonstration of high precision 
very high resolution tomographic SAR inversion with the 
assistance of TanDEM-X data. The data quality of TerraSAR-X 
and TanDEM-X is investigated. TomoSAR algorithms such as 
SVD-Wiener, Nonlinear Least Squares and SLIMMER are 
extended for mixed repeat- and single-pass data stacks. A 
systematic approach is proposed for the fusion of TerraSAR-X 
and TanDEM-X data in which the different data quality 
provided by the TerraSAR-X and TanDEM-X data are taken 
into account by introducing a weighting according to the noise 
covariance matrix. The proposed approach is evaluated with 
simulated data. The simulation result shows that the 
reconstruction accuracy of tomographic SAR inversion can be 
improved significantly by using jointly fused TerraSAR-X and 
TanDEM-X data. 
Future work will concentrate on real data demonstration: the 
system approach for measurement noise matrix estimation of 
  
  
Figure.1. 3- 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
   
mixed TerraSAR-X/TanDEM-X data stacks will be 
investigated; real data processing examples of mixed 
TerraSAR-X/TanDEM-X data stacks will be presented, the 
estimation accuracy increment will be quantitatively studied. 
REFERENCE 
Deledalle C., Denis L., & Tupin F., *NL-InSAR: Nonlocal 
interferogram estimation", IEEE TGRS 49 (4), pp.1441-1452, 
2011. 
Fornaro G., Reale D., and Serafino F., “Four-dimensional SAR 
imaging for height estimation and monitoring of single and 
double scatterers," IEEE TGRS 47 (1), pp. 224—237, 2009. 
Lombardini F., Differential Tomography: A New Framework 
for SAR Interferometry, in Proc. IGARSS, pp.1206—1208,2003. 
Zhu X. and Bamler R., *Very high resolution spaceborne SAR 
tomography in urban environment,” IEEE Trans. Geosci. 
Remote Sens., vol. 48, no. 12, pp. 4296-4308, Dec. 2010. 
Zhu X. and Bamler R., *Demonstration of Super-Resolution for 
Tomographic SAR Imaging in Urban Environment," IEEE 
TGRS, in press. 
Zhu X. and Bamler R., “Super-resolution power and robustness 
of compressive sensing for spectral estimation with application 
to spaceborne tomographic SAR," IEEE TGRS, vol. 50, no. 1, 
pp. 247—258, 2012. 
Zhu X., Very High Resolution Tomographic SAR Inversion for 
Urban Infrastructure Monitoring — A Sparse and Nonlinear 
Tour.,Deutsche Geodátische Kommission, Reihe C, Nr. 666, 
Verlag der Bayerischen Akademie der Wissenschaften, ISBN 
978-3-7696-5078-5, 2011 
Zhu X. and Bamler R., “Let’s do the time warp: Multi- 
component nonlinear motion estimation in differential SAR 
tomography,” IEEE GRSL, vol. 8, no. 4, pp. 735-739, 2011. 
Zhu X. and Bamler R., “Tomographic SAR inversion by L1- 
norm regularization—The compressive sensing approach,” 
IEEE TGRS vol. 48, no. 10, pp. 3839-3846, 2010. 
view of the scatterers reconstructed by TomoSAR reconstruction of city blocks in downtown Las Vegas, using a 
stack of 30 images acquired by TerraSAR-X. Height is color-coded.